Calling circuit



Feb. 7, 1933. R. D. GIBSON 1,896,487

CALLING CIRCUIT wip-f A7. D. G/BsoN @Y Feb. 7, 1933. R, D. GIBSON V CALLING CIRCUIT Filed April 18, 1930 2 Sheets-Sheet 2 Q Il@ MNM mm. NX QE J Q.

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Cy/Mf u ATTU/P/VEY vfor communication systems Patented Feb. 7, 1933 ROBERT D. GIBSON,

LABORATORIES, INCORPORATED, OF YORK, N.

YORK y CALLING Appupatio mea' April 1s,

This invention relates to calling circuits and particularly to -selective calling circuits for power-line carrier-current communication systems.

One object of the invention is to provide a power line carriercurrent communication system that shall effect selective calling of a distant station by a code signal of carriercurrent modulated with impulses-ofcurrent having more than one frequency within the voice frequency range.

Another object of the invention is to provide a power line carrier-current communication system having a plurality of signal stations connected thereto that shall eect selected calling between stations by transmitting a code signal of carrier-current modulated with impulses of two currents within the voice frequency range and -that shall insure against operation of the calling selectors at the signal stations during communicatlon between stations.

In a power-line carrier-current communication system of the type disclosed in thel patent to C. N. Nebel 1,7 33,553 dated October 29, 1929, communication is effected in opposite directions between stations by currents within the same frequency range. Ina system of this type it is desirable to have the impulses of currents employed for selectively calling a station to be withinthe same frequency range as the currents employed for communication between stations. It is desirable to have the communicating and calling currents within the same frequency range by reason of the transmission limitations of a power line.

In the present invention calling circuits are disclosed for a power line ca-rrier-current communication system of the type disclosed in the above mentioned Nebel patent'. *Calling between stationson the power 'line is effected by impulses of current of two frequencies within the voice frequency range. In the preferred modification of the invention two calling oscillators are provided at each station having frequencies within the voice frequen cy range, as for example, one oscillator may develop current having a frequency of 900 4patent having carrier-current modulated j with Y.; A oonrona'rron'or Nnw oIncUrr l i939. serialv'no. 445,275.

cyclesand the other* oscillator may develop" having a. frequency of 1500 cycles.

The two oscillators during Acalling of- OF RAHWAY, N'EW JERSEY, 'ASSIGNOR TO BELL TELEPHONE a distant station are'connected according to' a code signal to a transmitting channel of the type disclosed in the above mentioned Nebel ting only one the second modulator. Upon removalof the receiver from the switchhook at a calling station the two oscillators are energized but are notconnected at this timeto the transmitting channel; Upon operation of ya selector key, means is provided for intermittently connecting the two oscillators to the transmitting channel in accordance with vthe code signal to betransmitted. The code'signal of impulses of current of two frequencies supplied to the transmitting channel'are modulated by the two modulators in the transmitting channel in the manner disclosed in thefabove mentioned patent to C. N. Nebel.- The selector key also controls the local selector at the calling station to give the calling operator.l

thecode signal transmitted. Y

an indication o-f Each of the stations-connected to the-power line is provided with a receivingfchannel of the type disclosed in the patent C. N. Nebel. The receiving channel is provided with two demodulators for demodulating the received' K l modulated current to obtain voice frequency currents. In the present invention two rectiiiers and two tuned circuits areconnected in 'parallel to the output circuit of the second demodulator. The two tuned circuits are re.- spectively tuned to the frequencies of the two calling oscillators. sociated with the tuned circuits control a relay and the two relays jointly control the operation of a selector magnet. The selector` magnet operates a local selector. In 'order to operate a selector magnet andthe local selector at a called station itis necessary to re- Vceive a code signal of impulses of current having two different frequencies. Thetuned circuits connected to the receiving channel at a called station in each casebeing tuned to the same frequency as the calling oscillatorsata two modulators and transmit-V side band of the output from Each of the rectiers asf 'fied calling station. In a system of this type it is apparent that the currents employed during communication between two signal stations will not be able to simultaneously transmit voice frequency currents through the two tuned circuits for operatin g the selector magnet and the selector in accordance with any code signal. v Each of the stations is provided with means for.V disconnecting thetwo tuned circuits from the'receiving channel. Such means is preferably operated upon removal of the receiver from the switchhoolr.

In the accompanying drawings Figure-1 is a diagrammatic view of calling circuits constructed in accordance with the invention;

Fig. 2 is a Vdiagrammatic viewof a modicalling circuit. Referring to Fig. 1 of the drawings a signal Y station comprising a transmitting channel 1 anda receiving channel 2 is connected' by a coupling filter 3 to a power line comprising conductors 4, 5 and 6. vThe transmitting channel is provided with two modulators 7 and 8 and the receiving channel is `provided with -two demodulators 9`and 10. "The modulators .7 and 8 and the demodulators 9 and 10 are similar in construction and operation to the `modulators and demodulators shown in the above mentioned patent to Nebel.

An operators telephone set comprising a receiver-11 and a transmitter 12 isconnected -to thetransmitting channel 1 and thereceiving channel 2 by means of arhybrid coil 13. The receiver controls the vswitchoolrv whichopcrates an auxiliary switch 14. The switch 14 upon the removal of the receiver from the switchhoolr completes a circuit from abattery 15 through a filament relay 16. i The filament relay 16 completes circuits not only for energizingcalling oscillators 17 and'18 but also for heating thevarious thermionic tubes (not shown) which are utilized at the station. A `complete description of the operation of energizing the various thermionic tubes upon re- Inoval of the receiver from the switchhook is given in the above mentioned patent to Nebel.

The two calling oscillators 17 and 18 which are controlled by a pulsing relay 19 are pro.- `vided for transmitting -a code signal of impulses of vtwo currents within the voice frequency range. with theimpulses from the oscillators 17 and 18 by means of the modulators 7 and 8.' VPreferably, the oscillators 17 and 18 are of the thermionic type. The pulsing relay19 is provided with two switch members 2O and 21. Switch member 21 serves to connect the oscillators 17k and 18 across thetransmitting channel 1 when the relay 19 is in an operative posi,- tion. Switch member 2O completes a. circuit from battery 22 through the selector magnet 23. The selector magnet 23 operates a selector 24 for completing a circuit to operate a call `82 and 29, respectively, of two relays and 31. .and 31 have their switch 18. VThe relay 28 opens Aoperation is transmitted Carrier current is modulated' former and tuned circuit 27 is connected to a rectifier 29 by a transformer'. `The rectifiers control theoperation The two relays 30 members connected in series for completing a circuit from the battery 22,'through the selectormagnet 23.

If the operator desires to call a distant station he first removeshis receiver from the switchhook. Upon removal of the receiver from the switchh'ook the switch 14 completes a circuit from-the battery 15 for operating the filament relay 16 and a circuit from the batteryv 30 for operating the relay 28. Filament relay 16 energizes the calling selectors 17 and the circuit connection between the tuned circuits 26 and 27 and the receiving channel 2. A selector key 31 of the type shown Vin the patent to VJ. C.y Field '#1,354,814 dated October 5, 1920,*is operated in accordance with the code signal required to call the distant station. ,The pulsing relay 19 is operated tov connect the oscillators 17 .and 18 jointly toA the transmitting channel Yaccording to the code signal. Carriery current ismodulated with the impulses from the oscillators 17 and 18 bythe modulators 7 and 8 and one side band of the second modulation over the power lines as disclosed in the above mentioned patent to Nebel.. rThe relay 28 serves to prevent operation of the relays 30 and l31 by the impulses which are transmittedfrom the oscillators 17 and 18. However, the switch member 20 which is operated by the pulsing relay 19 serves to operate the selector magnet 23 in accordance zwith mitted. .y

At the called station the modulated code signal is demodulated by the demodulators v9 and 10. "The voice frequency currents having the same frequency as the currents from the oscillators 17 and 18 are selected by the tuned circuits 26and 27.- Such currents'are rectified by the rectiiiers 82 and29 for operthe` code signal being transating the relays 30 and 31. The relays 30 yand 31`operate the selector magnet 23 in acc'orda'nce with the code signalfor completing the circuit through the selector to operate the bell 25. `The selector 24 at the called station is operated .by the 17th impulse and the 18th impulse serves'to release the selector. Upon removal of the receiver from the switchhook at the Vcalled station the relay 28 is operated, but by this time the .code signal has been completely` received andno harm 26 and 27 from the receiving channel.

is done by disconnecting the tuned circuits The Y pulsing relay 19 at both the calling and called A contacts 41 andoi normal contacts 42 is provided for controlling the operation of a pulsing relay 43 by means ot' an oil-normal relay 44 andA a control relay 45. The control of the pulsing relay by a telephone dial switch is very similar' to the control means disclosed in the application of H. B. Arnold and L. B. Cooke, Serial No. 445,077 ,tiled April 17, 1930.

AThe dial switchis provided witha cam member 46 which operates the pulsing contacts 41 at just half the speed, such contacts are operated by the usual ligure 8 shaped cam member. With a dial .switch so construct/ 51 the pulsing contacts may be left in open or closed position and accordingly means must be provided for insuring that the pulsing relay 43 is always deenergized when conversation tales place between the calling and called station. Furthermore, means must be provided to insure the transmitting of correct code signal irrespective of the initial position of the pulsing contacts.

The pulsing relay 43 comprises two coils 47 and 48, and two switch members 49 and 50. Switch member 50 controls the connection of the oscillators 17 and 18 to the transmitting channel 1 and switch member 49 controls the operation of the selector magnet 43. The off-normal relay 44 comprises coils 51 and 52 and two switch members 53 and 54. The control relay 45v comprises two coils 55 and 56 and three switch members 57, 58 and 59.

The selector 24 operates a relay 60 having three switch members 61, 62 and 63. Switch member 61 completes a circuit from a bat tery 64 for operating the bell 25. The switch member 62 completes a holding circuit from the battery 15 for the relay60. The switch member 63 completes a circuit from battery 65ior operating a relay 66. The relay 66 is provided with two operating coils 67, 68 and two switch members 69 and 70. The switch member 70 serves to complete a circuit from battery through the coil 47 of the pulsing relay 43 to disconnect the oscillators 17 and 18 from the transmitting channel at the called station during conversation. The switch member 69 completes a holding circuit through the coil 68 of the relay 66 when the receiver at the `called station is removed from theswitchook.k

If the operator desiresto call a 'distant station he iirst removes his receiver from the switchhook and operates the auxiliary switchi 70v 14. Y Thereupon, the filament relay 16 and the relay 28 are operated. The ilament relay 16'energizrs the oscilators 17 andl 18 and the relay 28 disconnects the tuned circuits and 27 at the calling station'from the receivingfj channel v2.

Assuming the pulsing Contact 41 of the dial switch to be in open position and the dial switch to be operated to transmit a code signal, a circuit is completed by the off nor- 580 mal contacts 42 for operating the oH-normal relay 44. The circuit completed bythe offnormal contacts may be traced from battery 76 through the switch 14, ott-normal contacts 42, coil 51 of the ofi-normal relay 44, switch C85 member 59 of the control relay 45 and ground return to the battery 76. rlffhe` off-normal relay 44 is operated' and a holding circuit -is co-mpieted by the switchfmember 54 through y the coil 52 and the auxiliary switch 14. The pulsing contacts 41 ofthe dial .switch operate the pulsing relay 43 by a circuit which may be traced from the battery 76 through the auxiliary switch 14, pulsing contacts 41, switch member 53 oftheo'tlnormal relay 44, coil 48 of the pulsing rela' 43 and ground return to the battery 76. y pon completion of this signal the pulsing contacts 41 are closed to insure the operationlofthe pulsing relay 43 so as to disconnect'the oscillators 17 and 18 300 from the transmitting channel 1. The. selector magnet 23 is operated by the switch memj ber 49 of the pulsing relay in order to operate the selector at the called station and give the roperator at such station an' indication-ot the signal being transmitted. A

At the called station the modulated impulses comprising the code signal are demodulated by the de'modulators 9 and 10. The Vcircuits 2,6 and 27 whichare tuned to the same frequency as the osci'lators 17 and'18 select the code signal impulses *which are transmitted to the rectiiiers 82 and 29 for 'operating the relays 30 and 31. The relays 30 and 31Yelect the operation of the selector magnet 23 which, in turn, operates the seleci tor 24 for operating the relay 60. AThe relay 60 completes a circuit for operating the called bell 25. The switch member 62 as before set forth completes a holding circuit for the relay 60 from a. battery 15 through the switch member of the filament relay 16. The switch member 63 completes a circuit from the batteryV 65 for operating relay 66. The switch member 7 0 ofV the relay 66 complete/s a circuit for operating pulsing relay 43 to insure the disconnection of the oscil-y lators 17 andY 18 Y 'from the transmitting channel at the called station.Y The switchI member 69 completes a holding circuitfor the 130 `los fue

als

relay 66 when the receiver is removed from the switchhook. v Y

When the operator at the called station removes his receiver from the switchhook a Y 5 circuit is completed from the battery 76 for operating the filament relay 16 and the relay 28. The filament relay 16 opens the holding circuit through the relay 60 to stop operation of the call bell 25. The relay 66 and the 'f 10 pulsing relay 43 are not released at this time by reason of the holding circuit through the relay 66 which is completedby the switchV closed position and the operator desires to call a distant station, he lirst removes his receiver-from the switchhoolr and a circuit is completed for operating the control relay 45. The circuit for operating the control relay may be traced from the battery 76, through the auxiliary switch 14, pulsing contacts 41, coil 55 of control relay, switch member 54 and ground return to the battery 76. The pulsing relay 43 is not operated this time inasmuch as the pulsing contacts 41 of the dial switch established a shunt circuit across Vthe coil 48 of the pulsing relay 43. The shunt circuit across the coil 48 may be traced from one terminal of the coil through switch memfrm ber 58, pulsing contacts 41 of the dial switch and switch member 57 to the other terminal of the coil 48. Upon separation of the pulsing contacts the shuntcircuit across the coil 48 is opened and such coil is energized from the battery 7 6. The energizing circuit for the coil 48 of the pulsing relay may be traced from the battery 76, throughy the switch 14, switch member 57, coil 48 and ground return to the battery 76. Upon completion of the code signal the pulsing contacts 41 of the dial switch are held in open position to insure the operation of the pulsing `relay 43 to disconnect the oscillators 17 and 18 from the transmitting channel 1. y

The operation at the called station when the pulsing contacts of the dial switch are initially closedis the samel as that before described when the dial switch was considered with the pulsing contacts initially in open position. Y Upon completion of the conversation between the'called and calling station., the replacing of the receivers upon the switchhools open the auxiliary switch 14 for releasing the control relay 45 and the relay 60 to return all parts to normal position.

Modifications in the systems and in the arsignal of carrier current modulated with impulses from each of said oscillators at a calling station to call a distant station, control means connected to the line at a called station comprising two circuits each including a filter, a rectifier, and a relayV and responsivev only to said code signal transmitted from the calling station for operating the selector at the called station, and means for disconnecting said control vmeans from the line upon .removal of thereceiver from the switchhook.

2. In a signal system', a transmission line havinga plurality ofrsignal stations connected thereto, and means for effecting selective calling between stations by code signals of carrier current modulated with two currents of audio frequency comprising calling selectors at said stations, a `plurality of relay means connected to the line at each station, means at a called station for demodulating a received code signal of modulated current impulses tov operate said relay means, each of said relay means responsive to impulses of audio frequency current of a particular frequency dierent from the frequency of the impulses operating the other relay means, means controlled by the joint operation of the relay means at a station to effect operation of the associated selector, and means at each station for disconnecting the relay means from the line upon removal of the receiver from the switchhook.

3. In a signal system, a transmission line having a plurality of signal stations connected thereto, means at a calling station for transmitting code signals of carrier current modulated with two currents of audio frequency to a called station, calling selectors at said stations, transmitting and receiving channels at each station, a plurality of relay means connected to the receiving channel at each station, means at a called station for deniodulating a received code signal of modulated current impulses to operate said relay means, each of said relay means responsive to impulses of current of particular audio fre- -z quency different from the frequency of the impulses required to operate the other relay means, means ata calling station for transmitting a code signal ef impulses of currents of different frequencies to operate the relay e'. In a signal system, a power line having a plurality of signal stations connected thereto, calling selectors at said stations, means at a calling station to simultaneously transmit to a called station code impulses of cartor, and means at a calling station operated upon removal of the receiver from the switch- .hook for preventing operation ofthe two separate control means when transmitting a signal.

In witness whereof, I hereunto subscribe my name this 17th day of April, 1930.

` ROBERT D. GIBSON.

rier current modulated with two voice fre- ,Y

quency currents, means at-the called station to demodulate the received calling code signal, selective means comprising filters for separating the code impulses of the two voice frequency currents transmitted from the calling station, rectiiers respectively connected to the output circuits of said filters, and means comprising two relays respectively connected to said rectiiiers for jointly operating the selector at the called station.

5. In a signal system, a power line having a plurality of signal stations connected there to, calling selectors at said stations, two calling oscillators at each of said stations, each of said oscillators developing a frequency within the voice frequency range, each station having a transmitting channel for modulating carrier current with voice frequency current and a receiving channel for demodulating received modulated current, means at a calling station for energizing the calling oscillators upon removal of the receiver from the switchhook, means for simultaneously connecting the two calling oscillators to the transmitting channel in accordance with a code signal to transmit carrier current modulated with impulses from the two oscillators, two filters at the called station respectively selective of the frequencies of the two calling oscillators at the p calling station and connected in parallel to the receiving channel, a

rectifier and relay in the output circuit of each of said filters, means jointly operated by said relays for operating a calling selector at the called station upon receipt of thetransmitted code signal, and means for disconnecting said filters'from the receiving channel upon removal of the receiver from the switchhook.

6. In a signal system, a power line having a plurality of signal stations connected thereto, means at said stations for transmitting code signals of carrier current modulated with impulses of two voice frequency currents for selective calling purposes, means at said stations for demodulating received code signals, means comprising lters ing the impulses of the two voice frequency currents, two separate relay means operatedby the received impulses of the two voice frequency currents for operating a calling selecl no 

